This invention relates to information movement within a data processing system generally between a memory unit of the data processing system and a peripheral, and more specifically, relates to a microprocessor based input/output (I/O) controller.
Microprocessor based systems, especially those used as intelligent peripheral controllers, are often faced with a time critical data movement problem. In its simplest form, this problem is one of moving data from a buffer in a peripheral controller device (which appears to the microprocessor as a single location in a memory map) to an ordered array of sequential locations in memory (RAM).
In present systems, the peripheral controller device is usually equipped with a control line to indicate that data in the buffer is ready to be moved. This control line is usually connected to an interrupt terminal of the microprocessor. Upon the occurrence of a data ready signal at the interrupt terminal, the microprocessor causes a plurality of operations to be performed. These operations include saving the state of the machine (i.e., the microprocessor). Data is moved from the buffer of the peripheral controller to an internal register of the microprocessor. Next, an index register is loaded with a previously saved pointer, and then the data is moved from the internal register to a location in a RAM pointed to by the index register. The quantity in the index register is incremented and saved for the next data movement, and finally the machine is restored to the state existing before the interrupt occurred.
If there is sufficient time to execute all of these steps before the peripheral controller device has a data over-run, this method of data movement is simple and works very well. But, as data transfer speeds increase, especially in high density floppy, winchester or communications applications, the microprocessor will run out of time to perform all of the above operations before the next piece or quantum (usually a byte or a word) of data is available.
Hence, there is a need to provide an apparatus for performing the desired data movement at the high speed transfer rates required in the aforementioned applications.